In recent years, miniaturization of cameras such as digital still cameras has rapidly progressed, and mobile phone devices having small cameras have rapidly spread in the market. Hence, there has been an increase in demand for the strobe apparatuses employed as auxiliary light sources for photographing, and it is required to further decrease the size thereof.
The strobe apparatuses are a type of discharge devices, and such a conventional discharge device will be described as follows.
(Conventional Technology 1)
In the strobe apparatus that is one of the conventional discharge devices, as disclosed in Japanese Unexamined Patent Application Publication No. 7-85988, a main capacitor is charged by at least stepwise or continuously switching among appropriate driving pulse widths and duty ratios on the basis of a battery voltage at the time of driving a primary side of a separately-excited strobe charging circuit, a battery voltage in the middle of the charging operation, and charging voltages in the beginning and middle of the charging operation of a secondary side main capacitor.
In a strobe apparatus disclosed in Japanese Unexamined Patent Application Publication No. 2004-6083, a state of a battery right before being charged is detected by a microcomputer and the microcomputer controls a driving pulse width depending on the state of the battery such that overcurrent does not flow in the battery.
(Conventional Technology 2)
In a conventional strobe apparatus (see Japanese Unexamined Patent Application Publication No. 5-316729), a separately-excited DC/DC converter adopts a driving system in which the converter outputs a signal by comparing a charging voltage of a main capacitor with a triangular-wave voltage having a low frequency outputted from a triangular wave generator and converts the output signal into a PWM signal for driving. In the conventional strobe apparatus, when the charging voltage is excessively low at a starting time, the converter lowers a driving frequency relative to a static driving frequency so as not to cause overcurrent, thereby driving a battery with the pulse width in a turn-on period being decreased relatively for each control cycle.
In another conventional strobe apparatus (for example, see Japanese Unexamined Patent Application Publication No. 11-84484), a separately-excited DC/DC converter performs a PWM control by using a micro computer. In this conventional strobe apparatus, when a charging voltage of a main capacitor is excessively low, the converter does not change a control cycle so as not to cause overcurrent and decreases a pulse width for driving, compared to a case where the charging voltage is in the static state.
In another conventional strobe apparatus, (for example, see Japanese Unexamined Patent Application Publication No. 11-87083), an inrush current at the time of oscillating a transformer for charging a main capacitor is controlled by using a separately excited fly-back mode. In the conventional strobe apparatus, when a relatively high detection value is detected by a charging voltage detection circuit that is used for detecting a charging voltage of the main capacitor, a CPU controls generation of an output pulse so as to reduce a charging time of the main capacitor such that a pulse width of a strobe pulse signal, which is output from a strobe pulse signal generation circuit, for driving the oscillation transformer relatively increases or a pulse period of the strobe pulse signal relatively decreases.